This invention relates to a method for making matt finish coatings which can be classified on the Boller gloss scale as type 258, which 20 to 50%, (i.e. from matt to half-matt/half-gloss) on the basis of powder varnishes of 1,2-epoxy compounds and salts of polybasic carboxylic acids and cyclic amidines and conventional additives such as leveling agents.
Powder varnishes are being used increasingly for making coatings. Powder varnishes are finely powdered synthetic compositions containing a thermosetting compound, mostly a resin, a cross-linking agent, i.e. hardener and additives such as pigments, dyes, fillers, leveling agents and so on.
Among the thermosetting powder varnish systems, coating powders based on epoxy resins are used predominantly.
By using common hardeners like amines, acid anhydrides, boron trifluoride complexes, polyamino amides, dicyandiamide or substituted dicyandiamide, coatings with more or less high gloss finish are produced.
For special fields of application, for example smaller surfaces, glossy or half-glossy coatings are desired. Objects of large surfaces, however, are supplied with matt or half-matt finish coatings in order to avoid undesirable or unsuitable reflections of light.
In order to obtain a matt surface finish, matting agents like particulate (micro) silicic acid, talcum and so on must be worked into the composition. It is often a problem to work with materials having different densities which can lead to undesirable separation of the coating mass, to working difficulties and/or differences in coating quality.